Very impressive performance and built like a tank. But realistically it would not be used much. I find wide angel shooting to be very challenging and almost believe this talent resides in a disconnected part of my brain.
Like Bryan says in the review; Making a good picture is fairly easy, making a great one is extremely difficult.
The preferred alternative for me, the 17 TS-E 4L has the immense advantage of being a tilt&shift lens. That way I can correct for many of the perspective problems I often have. This is also an optically absolute top performer and I doubt I will miss having the 2mm extra very often.
And I believe I have heard a rumor .... of a 14-24L ...(?)
1DXII, 5DIV, 5DSR, 8-15/4L, 11-24/4L, 16-35/2.8L III, 24-70/28L II, 70-200/2.8L IS II, 100-400/4.5-5.6L IS II, 200-400/4L IS 1.4x, 17/3.5L TS-E, 24/4L TS-E, 35/1.4L II, 100/2.8L IS Macro, 300/2.8L IS II, 600/4L IS II, Zeiss: 15/2.8, 35/1.4, 55/1.4 Otus, 85/1.4 Otus, Profoto B1